▁" although ▁they ▁did ▁not ▁receive ▁instruction ▁in ▁the ▁use ▁of ▁the ▁standard ▁algorithms , ▁the ▁children ▁in ▁the ▁Con struct iv ist ▁group ▁were ▁the ▁most ▁successful ▁at ▁both ▁two - digit ▁addition ▁and ▁sub tra ction ." ▁Many ▁research ▁reports ▁demonstr ating ▁the ▁success ▁of ▁the ▁program ▁are ▁critic ized ▁by ▁oppon ents ▁of ▁this ▁curr icul um ▁as ▁having ▁poor ▁method ology ▁or ▁for ▁being ▁conducted ▁by ▁the ▁publish er . ▁NS F - sp ons ored ▁curr ic ula ▁are ▁required ▁to ▁conduct ▁and ▁report ▁such ▁studies , ▁something ▁that ▁is ▁not ▁required ▁of ▁traditional ▁mathematics ▁text books . ▁See ▁also ▁a ▁recent ▁study ▁conducted ▁with ▁the ▁re vised ▁edition , ▁for ▁more ▁evidence ▁of ▁effic acy . ▁ ▁Some ▁school ▁districts ▁report ▁their ▁own ▁data ▁about ▁success ▁with ▁the ▁program . ▁ ▁Crit ic ism ▁ ▁Investig ations ▁initially ▁was ▁commer cially ▁successful . ▁But ▁parents ▁and ▁math ▁educ ators ▁have ▁critic ized ▁its ▁lack ▁of ▁traditional ▁arithmetic ▁content , ▁of ▁decimal ▁math , ▁of ▁multiplication ▁tables , ▁of ▁division ▁and ▁multiplication ▁of ▁fra ctions , ▁or ▁even ▁of ▁addition ▁and ▁sub tra ction ▁of ▁ordinary ▁fra ctions ▁apart ▁from ▁a ▁small ▁subset , ▁its ▁emphas is ▁on ▁" k inder g arten ▁activities " ▁( cut ting , ▁fol ding , ▁tap ing , ▁etc .) ▁in ▁class ▁and ▁home work , ▁its ▁lack ▁of ▁a ▁traditional ▁text book ; ▁its ▁in compat ibility ▁with ▁high - school ▁and ▁international ▁mathematics ▁methods ; ▁its ▁non - trad