The go-to learning portal for high school and college students is bulking up its curriculum.

Quizlet, best known for its flashcards and study tools, is acquiring education tech platform Slader, which offers detailed explanations of textbook concepts and practice problems. The platform is popular with millions of high school and college students who are looking for more in-depth guidance. The financial terms of the deal are not being disclosed.

The investment highlights the urgent demand for extra help and resources even as students return to classrooms.

"There has been an ongoing and growing need for students to be more self-directed. This need for self learning isn’t new and hasn’t been brought on by the pandemic, but we do see the support systems that students lost because of the pandemic. The crucial face-to-face access — speaking with a teacher five minutes before or three minutes after class...remote learning has put a spotlight on the issue," Quizlet CEO Matthew Glotzbach told Yahoo Finance.

On Wednesday, the Biden administration announced that $81 billion of the $1.2 trillion coronavirus relief bill is being distributed across the nation to "help schools safely and quickly reopen and meet the needs of all students." Secretary of Education Miguel Cardona said he hopes all schools will fully reopen by the fall, but emphasized the outsized tailwinds facing communities that have already been hit hardest by the virus.

“While schools continue to show us what’s possible as they work to open their doors and meet students’ needs, we know that we still have a lot of ground to go. We owe it to our students — especially students in underserved communities and students with disabilities — to get all our schools opened safely and to meet the social, emotional, mental health and academic needs of all students," he said in a statement.

'Effective studying'

Among other subjects, Glotzbach says Slader's impressive explanatory breakdowns in math and science will add immense value for its students, who are trying to understand the more granular ways to solve complex problems. Both Quizlet and Slader operate under a freemium business model, and the two are figuring out what a full integration will look like and may adjust pricing.

"We help people focus their time and attention on effective studying. Quizlet is in a unique position to conquer that overwhelmed feeling when it comes to self learning. We want to continue to grow the breadth of capabilities," said Glotzbach.

Quizlet, which was founded in 2005, now has over 60 million monthly active users across 130 countries. The company raised a $30 million Series C in May 2020, bringing the company's post-money valuation to $1 billion. In the U.S., Quizlet is used by two in three high school students and one in two college students, according to the company.

A pioneer of the now $76.4 billion educational technology market, Quizlet has been profitable and logged a strong 2020 as more students and parents searched for help amid remote learning.

"We're a healthy and growing company. We entered into the pandemic with a healthy philosophy. It put us in a great position financially. We continue to hire people, make targeted investments and acquisitions. We’re thinking and planning for the future. What course would best help us serve students? Going public is on the table," he said.

Melody Hahm is Yahoo Finance’s West Coast correspondent, covering entrepreneurship, technology and culture. Follow her on Twitter @melodyhahm and on LinkedIn.

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