A lot of the alleged scholarship money out there is almost Snopes'ian in scope...it's supposed to be there, it's rumored to be there you just have to look for it. Well, that is sort of true and sort of not....there are legitimate contests but there are also somewhat-shady companies willing to take your money to find contests supposedly tailor-made for your child(say, that your child has red-hair and your last name is Morris, well the 'company' supposedly has information about a full-ride scholarship to Harvard for red-headed children with the last name of Morris...you just have to fork over a substantial finding-fee
first).
In answer to your question about when the students in your household should to start going for the dough?...now. As in Right Now, as in never too young to start.
Here's one URL I found, but some of the links on their website are out-of-date:
http://homeschoolwriters.com/chart.aspx
I would suggest going for local stuff, where the odds are in your favor and the pool of possible applicants is smaller.
Check out your church/synagogue/house of worship...sometimes there are local or congregational scholarships your kid can apply for.
Sometimes essay contests are specific to a certain area, maybe your county/district/state.
Check out local business or alumni associations, etc...sometimes groups like the local Rotary Club or Kiwanis, etc., have scholarship money to give away.
Ask people in your school district what might be available.
If your child is older - like in high school - they should plan to write many of their essays for college apps & scholarship apps over the summer.
Be VERY aware of any and all deadlines for any types of financial aid or scholarships.
If there are any contests in the student's areas of interest:
They like making videos and entering a special-interest video could win a savings bond or even cash for college...
They like history and they could enter a project in the National History Day competition...
My point here is that if the contest is something they are already interested in, then they will be motivated to do something special for the event, they will have the prize of learning *and* they could also maybe win some $ for their efforts. Also, if during your research you become aware of some contests that have no local support (for instance the National PTA runs something called "Reflections" every year), then you could always volunteer to help run your child's school's involvement with that contest.
Good luck,
agnes!