"I Promise students were among those identified by the district as performing in the 10th to 25th percentile on their second-grade assessments. They were then admitted through a lottery."
There will be some amount of regression to the mean then. It would be best to compare these kids to the students who "lost" the lottery rather to all students.
Because I wasn't sure which end of the bell curve this was referring to, "10th to 25th percentile" in this article means students significantly below the median, not above it.