If you are exclusing children for nits, you are denying them their right to a public education (FAPE). No nit policies are neither law nor recommended policy and practice by well established groups such as AAP, NASN and Harvard School of Public Health. According to the research, more than 30% of the children school nurses exclude for nits, do not have nits (they have other small white things in hair), and many of the other 2/3s of the children have hatched nits (following treatment) , not viable eggs.
Head lice do not pose a danger to students, and studies demonstrate that screening for head lice in schools does not decrease the incidence of head lice and is not cost effective.
NASN Position Statement is at
http://nasn.org/positions/2004pspediculosis.htm
Harvard School of Public Health information is at
http://www.hsph.harvard.edu/headlice.html (and there's an excellent management chart for schools)
AAP Report is at
http://www.aap.org/advocacy/archives/septlice.htm
*21 Surprising Things You Might Not Know About Head Lice*
School Nurse Perspectives
http://www.snp.homestead.com