As a language teacher, nothing (in the classroom) gives me greater pleasure than hearing a child verbalising in the target language and even pushing themselves to go beyond simple structures; giving opinions and evening justifying them. Ultimately, by far the best thing, is hearing pupils experimenting and not being afraid to make mistakes.
One particular activity that I have used with my classes, which has more and more allowed children to move closer to what is desired, is the ladybird game. Pupils are given a picture of a ladybird (substitute for whichever animal the class desired, one of mine protested and asked me to change it to a spider…) and on each leg is a number (from one to six) with a picture, word or phrase. Pupils work in pairs and role a dice, they then say the information of that leg. Their partner then assesses if the utterance was correct or not and, if so, the speaker then places a tick by that leg on their sheet. Pupils take turns in rolling and speaking until one of the pairs has all of their six ticks. If a pupil roles a number that they have already rolled, then they have to say the utterance again but with more information.
The advantages of this activity is that it seems to really engage at least the pupils in our school into speaking because of the added element of competition and chance. Furthermore, it is really simple to differentiate, as you can have a range of sheets (laminated, so that they may be used again) to cater for the different abilities in your class. You could use a verb on each leg (six fits well in this case), a picture from which pupils should create a word, phrase or entire sentence (simple or complex, with opinions and justification). Furthermore, as pupils complete one sheet, you can easily move them, onto the next, more advanced sheet. Personally, I find the younger years tend to respond well to giving them all positive points, credits, merits or whatever system of reward is used at your school, and saying that these may be taken away if you hear any English used during the activity; in my experience this is highly effective. You can constantly reinvent the game too, so that pupils see it each time as a new game/idea.