We have to keep in mind the vast majority of students in Bulgaria takes additional private lessons, especially in a year of 'matura' or when they want to get into a high school or university. For getting into university the parents pay additionally years and years of expensive private lessons so their kid get prepared for the really though exams normaly several levels of dificulty abouve what they kids studied. These lessons at one hand give teachers additionally source of incomes but is very very hard for families to educate their kids, especially if you have more than one.
Karolinka was right that education is really appreciated in Bulgaria, most people are eager to get an university degree, I think we used to have one of the highest number of universitie degrees in world back some 10-15 years ago, I don't know how are the numbers now. It is almost a must to have such if you want to have a better chance for cereer here.