I suggest searching past threads on portfolios. As you will see, it is much easier to get in with achievement testing than with a portfolio. I think you will see many people displeased that their dc did not get accepted with a portfolio and ended up doing the achievement or IQ testing route after being initially rejected. They had items 2-3 years ahead, but it is often difficult to show that a 6 year old is PG as opposed to HG with work samples.

Just my 2 cents.