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@AnnenbergInst posted RCT findings for Core Knowledge Charter Schools. Quick take: Notwithstanding study's claim of large effects, no discernible effect on English Language Arts (ELA) achievement in 6th grade (primary outcome) - although suggestive effects in grades 4 & 5.


  • Core Knowledge (CK) schools are public charter schools for students in grades K-8 that use an integrated curriculum setting out the specific knowledge students should gain in each grade. The CK curriculum is implemented at over 1,500 schools across 41 states and DC.

Study Design:

  • The study sample comprised 1,831 kindergarten applicants to 9 oversubscribed CK schools in Denver, randomized via lottery to treatment (admissions offer) vs control (no offer). The prespecified primary outcome was ELA score in grade 6 on state test.


  • No discernible impact on the primary outcome of 6th grade ELA - the effect size (ES) was near zero (0.04, not statistically significant). There were suggestive positive impacts in earlier follow-ups (4th grade ES=0.09 not statistically significant; 5th grade ES=0.12 and statistically significant).

  • The above results are the effects of winning the lottery & being offered admission. But only 45% of lottery winners chose to enroll. The effect on CK enrollees ("treatment on treated") was 0.09 in grade 6 - i.e., small/modest - but not statistically significant so could be due to chance.  


  • Based on careful review, this was a mostly well-conducted RCT. One modest limitation was sample attrition of 37% in 6th grade that falls within What Works Clearinghouse thresholds for acceptable levels of possible bias under optimistic but not cautious assumptions.

  • Disclosure: My former employer, Arnold Ventures (AV), helped fund this study. AV's summary of the study findings is linked here.

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