Microsoft is throwing open an advertisement-free version of its Bing search engine to all eligible kindergarten to 12th grade schools in the U.S., after completing the pilot stage of this program that was first run in five large public school districts.

The company is promising students an ad-free and safer search. After the no-charge “Bing in the Classroom” program is activated, Bing searches from within the school network will not have any advertisements, and will automatically and strictly filter to help block adult content. Microsoft will also disable the use of student searches for targeted advertising.

Microsoft’s catch-them-young strategy seems to have paid off as the program has grown to include hundreds of districts covering over 4.5 million kids in more than 5,000 schools, the company said Wednesday.

The company is offering students credits under the Bing Rewards program for searching with Bing from their home or mobile device. Students can choose which school to support with the credits, and once the school has earned 30,000 credits, a Surface tablet with Type Cover is sent directly to it.

“We created Bing in the Classroom because we believe students deserve a search environment tailored for learning,” said Matt Wallaert, creator of the program, in a statement. Classrooms should be ad-free both online and offline, he added.

Like Google, Bing runs an advertisement business around search. Bing’s search share grew to 18.2 percent while search advertising revenue grew 34 percent, Microsoft said in January. Digital analytics firm comScore reported this month that Microsoft sites had 18.6 percent of the share of search in the U.S. in March in comparison to 67.5 percent for Google sites.