I'm 15 and last summer I tried to lose weight. Well I did but I gained it back because after school when I get home I eat chips. XD So anyway. What I did was, I avoided bread and rice and other foods like that 'cause I hear they can cause fat even if they're healthy. And then try doing other kinds of exercise. I did 40 mins. of exercise 4x a week including using the jump rope, using my aunt's elliptical trainer, dancing, doing sit ups & stuff. So like in 40 minutes I get to do a whole lot of different kinds of exercise. And drink lots of water. Like if you're hungry, but it isn't exactly time for breakfast lunch or dinner yet, just drink a whole lot of water. Your belly might get big from drinking that much, but once you pee, it all comes out. You don't gain fat from water, I think.
So that was what I did. I didn't really measure my weight tho, because what I was aiming for was a smaller waistline, and I was able to do so. I think I lost like 4-5 inches in like a month & a half. I was happy with that. Too bad I have to do it all over again because I gained it back when school started again. XD Also keep a tally of your weight for every two weeks. And you can see if it works or not.
Hope I helped.