Natasha Singer for The New York Times:

DreamBox is among the minority of digital learning start-ups that have allowed independent academic researchers to examine and publicly report on their data. Still, the platform’s effectiveness is difficult to gauge.

A report from Harvard University’s Center for Education Policy Research concluded that DreamBox use correlated with some improved math scores. But, the researchers cautioned, if those students had more effective teachers even without the technology, “then we might be falsely attributing” student achievement gains “to the software, rather than to the teacher.”

Even so, Ms. Woolley-Wilson, DreamBox’s chief executive, described the study as good news, saying it confirmed encouraging reports from teachers. She pointed out that, unlike DreamBox, many other education start-ups lacked research to prove even the most basic assumption: that their apps did not harm students’ educational results.

Emphasis added.