Published on Organic Gardening (http://www.organicgardening.com)
Sow lettuce seed 8 weeks before the last spring frost to 9 weeks before the first fall frost. Seeds sprout in 4 to 10 days at 60° to 75°F. Grow seedlings at 55° to 75°F.
Links:
[1] http://www.organicgardening.com/seed-starting-lettuce
[2] http://www.organicgardening.com/learn-and-grow/lettuce-growing-guide