This rhyme is a useful way to start class, particularly for teachers who travel to others' classrooms. Instead of nagging students to switch gears, just start the rhyme, and they will join in! I expect students to be ready to start French class by the time the rhyme is over.
I start teaching it the first day, adding a line or two each class and checking for understanding as we go. Once we know it, I hand out a written version, which can be used for a range of activities including phonetic or conjugation study, translating, and a base for creating original sentences.
I write a new rhyme each year, and students remember and enjoy them years later! I have successfully used this in grades 3 to 9, varying the approach with the grade level.