I have two varieties of lettuce outside in my home garden. The red one is Marvel of the Four Seasons (Merville de Four Seasons), the green one is escarole Bionda A Cuore Pieno. I sowed the seeds for these indoors back in early March and transplanted them outside on April 11.
This year, I seeded my lettuce pretty dense in little flats, then transplanted them. (A flat that needs to be transplanted ASAP is on the lower right.) This way I'll get heads of lettuce, I hope. Last year I sowed the seeds directly in garden and found it difficult to thin enough to get heads. Nevertheless, the crowed plants made lots of delicious leaves.