The Compensation Hypothesis says that parents and prospective parents attempt to make up for lowered offspring viability by increasing reproductive effort to produce healthy, competitive offspring and by increasing investment in less viable, but still-living progeny (parental effects). The hypothesis assumes that offspring viability is lower when individuals are constrained (often through sexual conflict) to breed with individuals they do not prefer. We review results of experimental tests of the offspring-viability assumption in Tanzanian cockroaches, fruit flies, pipefish, wild mallards, and feral house mice. Experimental constraints on mating preferences lowered offspring viability in each of the studies. Females breeding under constraints laid more eggs or gave birth to more young than females breeding without or with fewer constraints on their mating preferences, and males mating under constraints on their mate preferences ejaculated more sperm than males mating without constraints. The number of eggs laid or offspring born was higher when female choosers were experimentally constrained to reproduce with males they did not prefer. Constrained females may increase fecundity to enhance the probability that they produce adult offspring with rarer phenotypes with survival benefits against offspring generation pathogens. Similarly, ejaculation of more sperm when males are paired with females they do not prefer may be a mechanism that provides more variable sperm haplotypes for prospective mothers or that may provide nutritional benefits to mothers and zygotes.