We systematically examine the existing evidence and compute meta-analytic averages for the effects of scaled-up, publicly funded pre-kindergarten (pre-K) programmes in the United States on student mathematics and reading achievement. The analysis is restricted to experimental and quasi-experimental research designs with the highest internal validity. We synthesise the short-term cognitive effects of pre-K and find large positive effects of scaled-up public pre-K programmes on student pre-kindergarten test scores from seven studies. In particular, we find that the overall effect on mathematics scores is over a third of a standard deviation and the overall effect on reading scores is three-fifths of a standard deviation. More research is needed on the sustained effects of pre-K as policymakers debate whether to expand or adopt such programmes.