First words sampler was probably one of the first apps that I purchased and used in therapy. I was almost in disbelief about how easy it was to get my clients to vocalize or use AAC (usually icon supports) to talk about what they saw.
The app itself is really simple: you drag letters blocks up to the visual match to spell a word. The app reads each letter as you drag it to spell the word out loud. Then, after the word is successfully spelled, the icon spins around.
I swear on my speech degree, that most kids will do anything (including vocalize, use full sentences to say what they see, expand sentences to include color) to see the icon spin around.
So, using this app to elicit language is easy! Simply hold the iPad and ask the student what he/she sees. After they state the one word ("cat") or expanded sentence ("I see yellow duck," "It's a blue ship."), then they can drag each letter into the correct spot and squeal with joy as the object spins around!
It's a sure thing, and free!