You have to ask more specific questions :)
Here are some ideas to help you prepare your debate on saturday:
-formal education has failed us in the way they try to make some stereotype on several things, as example, say that your teacher told you that people in 'country A' are not nice to foreigners, but in fact is that if you come visit that 'Country A', they are actually warm and kind. This might have been the result of some people who ever visited that place, they broke the rules and people in 'Country A' went mad at them, and then BOOM, these stupid people spread the words to the world
-formal education sometimes tends to restrict your imagination. as what i wrote above, those stereotypes things influence your imagination. you imaginations may similar to what the book has told you.
-most schools in indonesia are not trying to encourage you to use your ability. I mean, if you're a high-schooler, in grade 10, you have to take all science class and social class. grade 11 and 12, you;re forced to choose between science major or social major. Well think about this; how about if you like biology, chemistry, geography, and economics at the same time?
-last but not least, this is what just came to my mind: formal education sometimes forget the importance of informal education. i don't know whether Physical Education in school is classified as formal or informal, but i think every student need this! ah beside that, i believe that most of schools forget to include these important lessons (or may not be too important, but still important in future workplace or even your surroundings), they forgot to teach you how to develop your character, how to lead people and yourself, and how to act toward real situation (tired of just theories? so do i !)
Okay, those are my ideas. However, stay in school kid, formal education has much more benefits than the informal educations. informal education is just the tool that will helps you too face the actual problem on your daily life. Sorry if my answer is not too relevant and you expect better answers. Maybe you should come up with some original ideas too ;)
*hey why don't you try google-it? much more idea on google!!