You could rename the age groups to be something like "Entering 1st Grade," "Entering 2nd Grade," and so forth. That would be done from the "Age Groups" page in the settings section.
Another option would be to include a message on the form. This would be done from the "Forms" page in the settings section. You can create a new field on the student form labeled something like "Note to parents." You would want to define it as a "Display Only Text" field type, and enter your message in the content box. Once created, you can move it to just above the age group field.
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