Then, work out a plan to help them succeed. Let the boys experience the consequences of the truancy. Tell them calmly that this will happen if they choose to cut classes. If there is no truant officer, you might try going to school with them and following them through the whole day. This will usually stop the cutting of classes.
Teens just get too embarrassed.
I also know this means you would have to take off work and that's difficult, but my experience has been that it works and most parents find it worth taking time off. If you are experiencing many problems with your children, I urge you to enroll in a parenting class through your school. Family service agencies or sometimes juvenile corrections departments have them. These classes offer support and ideas on how to relate to your children. You can also check out some books or videos from your public library on parenting skills.