I would do it at the end of April for a few reasons...

1st, there's no need to sow them in early Winter

2nd, kids are really impatient! unless your daughter is doing several varieties (annual, perennial, cold-season veggie, etc) of seeds to WS throughout the winter season which will hold their attention, doing it closer to plantout date and/or end of school season will be quicker for satisifaction.

3rd) I'd suggest also doing another set of tomatoes inside and doing that project after the WS toms have sprouted, this was she has a comparison study. Have the kids plant both WS and inside-sown so they can learn the differences.

Thank you for your helpful comments.
Ann

Bloom buddie,
How wonderful your daughter is a teacher, My oldest daughter will be one too some day.
May I suggest dill instead, It sprouts so much earlier and is edible and the kids will definitely recognize the pickle taste.
Just an idea.
:)Laura

She might also want to consider having them grow calendula. They can be wintersown and they start sprouting just as winter's breaking. They can handle frosts after they sprout and flower in 8 - 12 weeks after they emerge.

Even in Wisconsin that should let them sow, sprout and flower all in the spring semester. The flower is nice and bright too:
{{gwi:444432}}

Swallowtail seeds has a bulk seeds section where you could get 2000 seeds for under $10. That would be enough for several years worth of winter sowing. The seed keeps well - I had close to 100% germination on 10 year old seed. (I never got around to sowing it because the seed packet photo didn't impress me - then I finally planted it and it was beautiful!)

Lynda

great Idea lynda,
then maybe they can give them to their mom's for Mothers day.
Even teens need to shop for moms.I know I'd love to get one of those beauties.
Bloom buddies, what grade does she teach? does she need some seeds? Maybe I/we can help. I love garden education for kids.
:)Laura

OOPS, Sorry Lynda, :)
I hate when names aren't capitalized.
Sorry Hon.
:)Laura
yeah I'm an OCD dork.

Good ideas, thank you. Will pass along your comments.

I'm going to have my first try at winter sowing this year too. I live in Oklahoma. Sorted through my seeds today and plan to sow mostly flowers.
Ann