ThinkCERCA, which offers a set of tools and lesson plans to help educators teach critical thinking skills, raised $1.5 million last June--but that’s not the end of it. Today, the Chicago-based company has raised $3.2 million in a Series A round led by the Follett Knowledge Fund, with Math Venture Partners, Amicus Capital, Great Oaks Venture Capital and Chuck Templeton also participating.

This marks the fourth investment for the Follett Knowledge Fund, founded in 2013 with $50 million on hand. But, according to Follett CEO, Mary Lee Schneider, the company is having a hard time finding the right investments.

“We have a standing pipeline of 30 to 35 companies that we look at,” Schneider tells EdSurge. “Only these four have met our criteria to date.” Other portfolio companies, in addition to ThinkCERCA, include ShowEvidence, ClassOwl and Vocabulary.com.

Schneider says she was impressed by ThinkCERCA’s “student-focused, educator-centric offering,” along with company CEO Eileen Murphy’s “healthy dose of skepticism” that technology alone can solve all of education's problems.

Founded in 2012, ThinkCERCA offers lesson plans and assessments that help educators teach critical thinking and analytic skills for any subject in grades 3-12. The company has paid subscribers in 215 schools, reaching 50,000 students in 25 states. Its free version is used by 115,000 students in 17,000 classrooms across the US and 112 countries.

“This investment, coupled with our strategic partnership with Follett….can help us scale our research-based approach to drive student outcomes, which is why we are so excited,” Murphy said in a prepared statement.

Follett, a major distributor of educational content and services, will help bring the tool to its network of 70,000 schools, says Schneider. She also sees a “a huge opportunity to combine ThinkCERCA with Vocabulary.com. Improving literacy, retention and critical thinking can be be a very nice integrated fit over time.”

Schneider says a “significant” portion of the $50 million Knowledge Fund is still up for grabs. Half of it is earmarked for early-stage investments; the other half is reserved for follow-on rounds, “which we have not tapped into.”