When my husband and I dropped our girl off at day care yesterday, the staff said that she had pushed herself up into the seated position. The only time we've seen her sitting was when we had put her in the position. She stays a while, then inevitably falls over and usually gets fussy because she'd rather be sitting. So, my husband or I usually make a beeline for her and set her back up. Maybe we've been way too quick to do so. Maybe she doesn't sit up by herself at home is because we never give her the chance.