Suthasri Wongsamarn, permanent secretary for education, told reporters she had instructed the Education Policy and Strategy Office to find out why students were not learning enough at school.
The findings would be used to improve teaching quality in classrooms and save students and their parents from having to cover the additional expenses of tuition classes, she said.
Ms Suthasri's order followed a call on Friday from National Council for Peace and Order chief Prayuth Chan-ocha for the ministry to place greater emphasis on improving teaching quality at schools to prevent families having to spend on tutorial schools.
In his weekly radio and television address, Gen Prayuth said many students chose to take on the extra burden of attending private classes outside school hours to increase their opportunities within higher education.
The Education Ministry should find out why they felt the need to do so, to help ease the burden on families, he said.
The permanent secretary for education said officials would investigate why students were seeking additional education outside of the classroom.
"The reasons could be because schools are failing to teach students well enough, or because tutors have given extra tips to students for completing their examination papers," she said.
''Another possibility is that students may want to increase their chances of enrolling at better universities."
"We need to find out the reasons so we can find the right way to correct the problem," she said.
Ms Suthasri said, however, if the students study hard in the classroom, they would not need to attend classes at tutorial schools.
She said students' academic achievements should be evaluated to assess not only what they learn in school, but also their knowledge of the skills they need to solve problems in the real world.