Even if measured IQ is highly variable before 3rd grade (I'd have to review the research on this), this is not a strong argument against identifying students in K, 1, and 2, as long as you also identify students in 3rd and later grades. Having multiple entry points should not be problematic, but whether students identified as gifted in 1st grade should also be assessed in later years and possibly removed from a gifted program is a difficult question. The Johns Hopkins talent search requires students who qualify by doing well on the SCAT in elementary school to do well on the SAT, ACT, Advanced SCAT, or Spatial Test Battery in 7th grade to maintain eligibility for various programs.