Any similarity to the author's normal avatars is entirely coincidental. No seriously. Like pressing the random button. This amuses me.
I realized that all my sims in Sims 3 tend to have mostly good and useful traits right from the start. When my sims raise kids, they always raise them well so they can pick good and useful traits. If they adopt a baby that has a bad trait or two, the kid grows up in constant happiness and soon gets enough lifetime happiness to change traits (through the oddly named Midlife Crisis, which is entirely unrelated to the actual midlife crisis that I belive was introduced with the Generations expansion.)
Enter Randon Dumey, a random dummy with the traits Absent-minded, Couch potato, Loser, Stupid. He started as a teen, because high school is a slog even for the gifted in Sims 3. I did not make him this way to enjoy watching his misery, but to prove to myself that even the disadvantages can acheive greatness if they follow the guidance of their higher-dimensional guiding spirit. (And have enough expansion packs, I guess. But the fairy tail only started after he finished his mandatory two weeks of high school. Even then it was seriously overkill and I wish I had a savegame from before it.)
The real poison was the Stupid trait: It made homework take more time than was availabble. Literally: Even when I got the MultiTab 6000 which makes schoolwork fun (and also several skills), there simply was not enough time to go to school, eat, pee, sleep and do homework. Not even when doing delayed homework at school. I found two solutions to this. First, coffee beans from University Life. They give a 3 hour joyful moodlet which also reduces energy loss to almost nothing for the duration. This means you can cut into your sleep requirements (but they don't last through a schoolday so get some sleep in the morning). The extra happiness let you save up for the 10 000 point MultiTasker lifetime reward, which lets you do homework faster (and also improves work performance, supposedly). The effect on homework was enough that I now could do them each day and still have some time left, although it did not fully negate the Stupid effect.
If you don't have University Life, you can cut down on sleep time with other expansion packs:
--Late Night: Mixology, energy drink. (But this takes a lot of practice, especially if you are stupid. Best used if there is a non-stupid person in the household, if you want to have it before the teen grows up.) Gives a mood boost and reduces energy loss, but not quite as much as coffee beans. On the other hand you don't get a negative moodlet after it expires. It grows more effective the more you practice making it, but again not the best for a single teen.
--Generations: Chemistry, sleep potion. It lets you sleep much more efficiently, a couple hours each night is enough. Again, this may take some time to get to.
--Supernatural: Alchemy, Invigorating Elixir. Requires wolfsbane. No joy moodlet, but gives a small amount of energy and freezes energy loss for 6 hours. I have gotten the recipe at the beginning or near the end, rarely if ever in the middle.
--Into the Future has a good number of synthetic drinks, I am not sure if any of these are useful for happiness (beyond Sugar Rush) or sleep reduction. By the time I got the last expansion pack, I was kind of loaded with mood boosters.
Skills: Logic is the most affected by stupidity, after a couple levels it starts taking sim-days to learn. Farming seems to be the least affected, so little that I am not sure whether it is slowed at all. (Perhaps in refernce to the stereotype of stupid farmers?) This allowed me to actually have lifefruit before I finished high school. In teens, eating lifefruit allows them to continue in high school longer, great if you had bad grades for the first week but still want to choose your adult trait. (I picked Eco-friendly, going with the gardener / farmer theme. Loves the outdoors is also good if you want to live by farming, fishing, and collecting (the latter is not a skill but still a good source of income, espeically if you have the collection helper or a macro like Awesomemod's from More Awesome Than You.)
--Late Night: Mixology, skill booster. It is the second standard drink, gives a mood boost and improves learning all skills by a modest amount.
--Supernatural: Alchemy, skill booster, gives a random increase to some skill, possibly one you have not started yet. Can be boosted by mixology skill booster for a larger gain. Vial of Enlightenment: Gives a similar random skill boost but you have to sleep / nap for it to take effect. Potent versions of them give more skill gain, half a level for the skill booster. I have not tried these with stupidity to see if they are reduced.
--Supernatural: Fairy has two auras that boost skill and can be used to counteract stupidity. One boosts art (painting, music, sculpture, writing, cooking) and one boosts body and mind (logic, athletics, martial arts,charisma, handiness, possibly science and future tech).
--Superntural: Vampire automatically learns all skills much faster during nighttime. Includes teens. Not tested if this affects homework speed.
Of course, you could just let your stupid sims remain stupid and watch them go about their stupid lives. But we get enough of that in real life, don't we? ^_^