It is fascinating to me to watch children grow, in both their abilities and their confidence. I think it is one of the pure pleasures of being a teacher.
It is not at all unusual for a new first grader to take several days, weeks, or even months, to observe what other children are doing before trying it themselves. They learn by watching older children, and notice how much pride and pleasure comes from accomplishment and effort. Mixed-grade classrooms are ideal for this sort of "reaching up".
One way I see this growth happen is our weekly poetry reading. We have a special poem in our anthologies for each week, and on Wednesday afternoons we take turns reading it. At first, a child may decide that they do not want a turn to read. That's fine, there is absolutely no pressure. (I usually stand by a child and simply run my finger along the words as another child reads them.) After a while, that same child may decide to take a chance, and a brave little hand will be raised. I ask, "Do you want to read it all by yourself, or all together?" Most times, a new participant will say, "All together!" and then the whole class will join in a choral reading. This is tricky, because our voices have to stay in tempo with each other. Finally, the child might raise their hand and want to read it "All by myself!", and with a flourish, jump up on their chair and read in a loud, clear voice. It's pretty great.
And, of course, several children take it one step further, and decide to memorize these poems. They proudly snap their anthologies closed, and give it a try.
There are all sorts of challenges in a classroom, and we take them on, step by step.