This is a tricky question--how to ask a teacher to accelerate work without appearing arrogant, or that you're a pushy parent, or "uber-mom". I have found that most teachers don't understand that I don't want MORE work, just more challenging work. I think teachers will either understand or won't. If they don't, there are a few choices: skip a grade, work at home at the higher level and have your child "endure" grade level work, or work with teacher and administration to see if they could do independent work (like ALEKS program, accelerated math, etc.). I have found that even the most understanding of teachers might have a problem with providing differentiated curriculum. My advice is to do as much groundwork as you can (e.g., for my 5 yr old, I ordered a workbook that I have asked be used in lieu of what they're doing in class).
