(a) In determining the number of employees of a school district for purposes of Sections 1579.151 and 1579.152, school districts that, on January 1, 2001, were members of a risk pool established under the authority of Chapter 172, Local Government Code, as provided by § 22.004, Education Code, may elect to be treated as a single unit. A school district shall elect whether to be considered as a member of a risk pool under this section by notifying the trustee not later than September 1, 2001.
(b) A risk pool in existence on January 1, 2001, that, as of that date, provided group health coverage to 500 or fewer school district employees may elect to participate in the program.

(c) A school district with 500 or fewer employees that is a member of a risk pool described by Subsection (a) that provides group health coverage to more than 500 school district employees must elect, not later than September 1, 2001, whether to be treated as a school district with 500 or fewer employees or as part of a unit with more than 500 employees. The school district must notify the trustee of the election, in the manner prescribed by the trustee, not later than September 1, 2001.
(d) For purposes of this section, participation in the program by school districts covered by a risk pool is limited to school districts covered by the risk pool as of January 1, 2001.