Summer vacation gives us a natural experiment to study the effects of vacation on IQ—and, unsurprisingly, the outcome is that one’s IQ is a function of what they are exposed to during the summer. We see the expected trajectories and outcomes in IQ based on the social class of the individual. A few studies since the 1920s/60s have been carried out on what occurs during summer vacation—and small, but noticeable—decreases in IQ are found. This only serves to further strengthen the claim that “IQ tests” are middle-class knowledge tests and that IQ is an outcome—not a cause.
Why may we see an IQ decrease in the summer? Well, for one, students are thrown out of the “school rhythm” that they get into the 9 months they are in school. Since they have three months they have off from their learning (say, June-September), when it then comes to test-taking, the students become less familiarized with these types of things, causing a decrease in scores. If “IQ tests” were indeed tests of middle-class knowledge and skills and if we think of an “IQ score” as a rough proxy of social class,, then we would expect that certain academic achievements related to IQ would raise or fall in certain contexts (i.e., one’s age, race, gender, social class, etc). This is what we find.
For instance, Cooper et al (1996) meta-analyzed 13 studies (while reviewing 39 studies). They found, due to summer vacation, student’s grade loss as tested before the summer and after was equivalent to losing one grade in that period of time. They also found that middle-class children had an increase in reading, while lower-class children had a decrease. This can be explained by, for example, the presence of books in the home and how they differ between social class. We know that the presence of books in the home is an indicator of academic performance (Evans, Kelley, and Sikora, 2014). This is important, because children who reported that they had easier access to books read more books (Kim, 2004), while voluntary reading programs do increase reading test scores (Kim and White, 2008).
“Growing up in the scholarly culture provides important academic skills“, note Evans, Kelley, and Sikora (2014: 19), and this is due to the fact that such tests are constructed by certain people with certain assumptions about the nature of the tests in question (Richardson, 2000, 2002). Thus, what explains the finding is the fact that those from higher-class families have more access to books, and so they avoid the decrease in reading skills during the summer. (Think of “summer reading” programs. I recall them from my youth. I remember reading The Hot Zone for a summer reading book once.) This replicates previous research from this team where they showed that children who grew up in homes with “many books” had three more years of schooling than children from “bookless homes”, and this was independent of the social class, education, and social class of the parent (Evans et al, 2010).
Cooper et al (1996) discuss Heyns’ (1978) book Summer Learning and the Effects of School where Heyns shows that summer learning is more dependent on parental occupation than is learning during the school year (Cooper et al, 1996: 243). Heyns’ data showed that summer vacation widened the gap in achievement between rich and poor (meaning high and low social class) and that it also widened the gap between blacks and whites. Cooper et al’s meta-analysis also showed that the gap in reading achievment between middle- and low-class learners during the summer was equivalent to a 3-month gap between them. While children in both classes show decreases in reading skills over the summer, lower-class students showed steeper declines than middle-class students. What this suggests is that class differences can—and do—in fact increase inequalities between the two classes. A lower-class status would then translate to being presented with fewer learning opportunities (meaning that they would have fewer opportunities to prepare for what amounts to middle-class knowledge tests), therefore explaining why the gap increases between the two social classes.
So, as Cooper et al (1996) show, summer vacation has an equal effect on math skills between middle-and lower-class children, while, when it comes to reading skills, lower-class students took a bigger hit (which can be explained by access to books in the home). So, to attempt to mitigate these disparities, we can, for example, mandate some type of summer math program for all classes, or instruction of reading for lower-class children since the analysis pointed to these two types of disparities. Of course, reading practice would be more readily available than math practice, which would explain why there is a disparity in differences between blacks and whites and between social classes.
Note that a decrease in mathematical skill was found by Paechter et al (2015) in a sample of Austrian children, who have a 9-week vacation. They write that “Losses or gains in a knowledge domain appear to depend on the degree of practice during the summer vacation“, and this is intuitive based on the nature of test-taking.
Entwisle and Alexander (1992; 1994) studied the “summer setback” between a random sample of blacks and whites in Baltimore, Maryland. In longitudinal fashion, they tested these black and white children before they entered the first grade. Math test scores were used as a proxy of how ‘stimulating’ a home was when it came to knowledge acqusition during the summer. They found that the two most important factors for math skills during the summer was that differences in family SES and how segregated the schools were. They also noted how school integration helps black students, and how white students do just as well, whether or not the school they are attending is integrated or not. (Also see Johnson and Nazaryan, 2019, who show the same—they also show that, regardless of race, children who attended integrated schools had better life outcomes than children who did not.) The 1994 paper also showed that linguistic differences between integrated Baltimore schools could also account for differences in reading skills. (Also see Patterson, 2015.)
Alexander, Entwisle, and Olson (2001) write (their emphasis):
When our study group started school their pre-reading and pre-math skills reflected their uneven family situations, and these initial differences were magnified across the primary grades because of summer setback despite the equalizing effect of their school experiences.
Class gaps grow in the summer, when “non-school influences dominate” (Condron, 2009) which, again, shows that these tests test certain types of knowledge found in certain classes over others which explains the disparities in certain things between groups. It is established that higher-SES children learn more over the summer (Burkam et al, 2004), and this is due, again, the types of content on the tests in question (since the tests are constructed by people from a narrow—higher—social class).
The lasting effects of the summer vacation learning gap is succinctly put by Alexander, Entwisle, and Olson (2007: 168):
(1) if the achievement gap by family SES during the elementary school years traces substantially to summer learning differences, and (2) if achievement scores are highly correlated across stages of young people’s schooling, and (3) if academic placements and attainments at the upper grades are selected on the basis of achievement scores, then (4) summer learning differences during the foundational early grades help explain achievement-dependent outcome differences across social lines in the upper grades, including the transition out of high school and, for some, into college.
Thus, summer vacation has a negative effect on all students, and this is particularly pronounced in differences between groups. So, we can either:
(1) Extend the school year; If we had a longer school year, we can then monitor children better and mitigate the problem areas that occur during the loss of school;
(2) Mandating summer school; If we had mandated summer school, then there would be less of an increase in academic achievement between classes, though such remedial classes have differing effects depending on context and the group studied (see McComb et al, 2001; Cooper et al, 2005).
(3) Make modifications to the school calendar. Since the hit to knowledge is not equal in all groups studied, then it would behoove us to target at-risk groups through the school year and then, possibly, have longer periods of breaks and not an all-at-once three-months off school as to better foster academic skills used for test-taking.
The heart of the problem of the ‘summer slide’ is due to less stimulating environments during the summer (which is different by race/social class), and thus, what explains the differences in amount of knowledge kept during the summer vacation is reflective of how well the household mimics the school environment since the tests in question are tests of middle-class knowledge and skills. This squares nicely with the research that schooling is important for IQ—even that it is causally efficacious regarding IQ (Ceci, 1990; Ritchie and Tucker-Drob, 2018). Even then, the gap between blacks and whites in test scores grows much more slowly during the school year than during summer vacation, indicating that “schools are, indeed, the great equalizers” (Downer, von Hippel, and Broh, 2004: 633)
This type of research does, indeed, buttress my claim that IQ is an outcome and not a cause. The claim that one is more ‘intelligent’ or that ‘one has a higher IQ than another’ (a claim that one is more ‘intelligent’ than another) is a descriptive and not an explanatory claim. We have at least three choices to think over when it comes to mitigating the problems that summer vacation brings to students—which is, relative to the school environment—‘duller’ environments which hampers learning and knowledge acquisition. Due to either lower levels of forgetting, or an advantage in continuing to learn over their less-advantaged peers, higher-SES children return to school with a subsequent advantage over lower-SES children and this is one way in which summer vacation widens inequalities between groups. Summer vacations, therefore, increase inequality between groups.