Any student who works hard and performs to the best of their ability deserves recognition. (Many times the easy learner is not working very hard and is not necessarily turning in his best work either.) My tendency would be to recognize this with a positive comment and/or a note of appreciation. Having an interest in them as individuals conveys to that student that they have value in your eyes.
We do not have an honor roll or special recognition for high grades so as far as effort goes the playing field should be even for all students.
I am cautious about rewarding students with a “participation prize” or similiar award just because they can’t make the grades of their classmates. After observing students over the years; I’m coming to the conclusion that we do students no favor if they are given credit (grade-wise or praise-wise) for unsatisfactory effort, just because they lack the ability of their neighbor.
However, take note of students who work hard. Write them a note that says “thank you for your good work”. Let them have the privilege of doing special things (errands, drill with younger students, design a bulletin board, put up art work, etc.) for the teacher.