That would be the best guess - overwatering - especially if in self watering containers. Seedlings shouldn't ever be left standing in water or prevented from drying out a bit as is only leads to root rot and nutrient uptake issues. I'd suggest you post this over on the Growing Tomatoes forum here since they have their own forum and include all the info you can about the potting mix used and what if any fertilizer you have given them. Dave

I have about 20 tomato seedlings going indoors, under T5 lights. They are in self watering pots and about 10" tall. A few are starting to get yellow spots...as shown in the photo. I think they may be over watered, but not sure if it's something else. I've stopped watering, and will let them dry out a bit. Any advice is greatly appreciated.

It's a sun scorch. Water droplet on the leaf magnifies the heat from lights or sun and burns the underlying tissue cells. It's no problem for the plant. Dave

"I can put the planting table on the back porch to place them on ..." How about a combination of the suggestions? Go ahead and take the table out there, but put the plants under it. Partial shade so that they don't get toasted when the sun is strongest, yet open to airflow and partial sunlight so that they will harden off. Then if it is predicted to get too cold, you can throw a sheet, blanket, plastic or rowcover over the table and have a mini green house. Bets