In what circumstances will a federal equal protection claim be successful against a state constitutional claim?

17 Although plaintiffs did not expressly ground this challenge on state constitutional grounds, the trial court in No. 29917 did base its preliminary injunction on both the federal and state grounds (i.e., Cal.Const., art. I, 11, 21, as well as art. XX, 18). Since we have construed the provisions of article I, sections 11 and 21 as 'substantially the equivalent' of the federal equal protection clause, our discussion of plaintiffs' federal challenge will also apply to any claim assertible under the state Constitution. (See Serrano v. Priest (1971) 5 Cal.3d 584, 596, fn. 11, 96 Cal.Rptr. 601, 487 P.2d 1241.)