Nasturtium Plants Turning Yellow

My kindergarten class is growing nasturtium flowers for mother's day. We have them growing under "grow" light that are on 24 hours a day. They looked great until 3 weeks into their growth cycle. Now all the leaves are turning yellow. What did I do wrong? Mother's day is coming up and I don't want to send home dead plants.

You did not mention what soil you have the plants growing in (they like well-draining fertile soil) and what fertilizing programme, if any, you were following. Fertilize with a complete fertilizer at every second watering. Also the weather is turning warmer now and the plantlets might be getting too hot. Make sure you have some cool air for them, especially at night. They may need some dark period, so you could try to give them eight hours of darkness by putting the lights on a simple mechanical timer.