I forgot to add that that it's certainly based on each child as well. My 4yr old is asking to learn her letters so we've been pointing them out as we read and since she is asking for "schoolwork" I've given her some prewriting worksheets and mazes. But I never push it-if she does it for 5 min or an hour-I let her lead the process for now.
Ann, Full-time mama of 2 crazy kids and a sling'n toddler