Nearly one in four US children speaks a language other than English at home. But there’s a shortage of bilingual teachers. So investors see opportunity. I’ve noticed a handful of investments in ed-tech startups offering ELL software this year (but more importantly, I’ve heard investors say that this is an area that they’re currently very keen on).

Language learning, and particularly English-language learning, isn’t just a matter of K–12 or US education. Other big names in the space: Pearson English, Open English. (Interestingly, there haven't been any language-learning investments this year, despite that being a very active space in the past. I think investors are really interested on what they perceive as this different group: that is, ELL students at the K-12 level.)