Actually my experience is just the opposite. Any head lettuce is easy to direct seed and then thinned to proper spacing and the thinnings eaten. Leaf lettuce can easily be started indoors in cell packs if you wish and is transplanted in clumps anyway as it doesn't require the spacing/thinning that head lettuce does. But neither type require starting indoors and both types often do better when direct seeded as you get higher germination rates.

Dave

My reasoning was to stagger harvest. We have a narrow window in spring as it is for decent lettuce production.

I direct sow and start under glass. (Unheated and no lights). Early direct sowing I do under a sheet of clear plastic laid over the soil. Either way the harvest is staggered because I sow in pinches of seed which require thinning. I transplant the thinnings and that means some seedlings get a bit retarded. Which is fine because I don't want them all maturing at once.

The thing is, for romaine or butterhead in particular, my household only needs a couple heads a week, max.

My kids won't touch lettuce, so it's only my wife and I eating it.

The main flaw with continued direct seeding is that germination will vary and drop to nil in mid summer. It is far more predictable to sew a six pack in your basement and transfer seedlings to garden 4 weeks later. Many commercial growers rely on that consistency: 4 weeks from seed to transplant; 4 weeks from transplant to harvest.

I just did that with some romaine that I just transplanted out. Should mature around the third week of October.