Section 27(5)(b) in The Representation Of The People Act, 1950
(b)every person who is ordinarily resident in a teachers’ constituency, and has, within the six years immediately before the qualifying date for a total period of at least three years, been engaged in teaching in any of the educational institutions specified under clause (b) of sub-section (3) by the State Government concerned, shall be entitled to be registered in the electoral roll for that constituency.