While at the University of Chicago, where he spent his academic life (1895–1934), Child experimented extensively with invertebrates such as planarian flatworms and freshwater hydras, which show a remarkable ability to regenerate themselves from small fragments. He observed that characteristic parts, such as a head or a tail, usually grew from that portion of the fragment where the same part had previously been joined, a phenomenon known as polarity. On the basis of his experiments, Child advanced a theory of antero-posterior dominance, stating that physiological activity in a multicellular organism increases along its axis from bottom to top (or tail to head), and that this gradient of activity in a tissue fragment determines the position of structures growing from it. He felt that the gradient was caused by the action of a chemical factor on cell functions. Although Child was not able to demonstrate how gradients were formed in the first place, his theory directed many investigators to seek to understand developmental processes in physico-chemical terms. Child was particularly influential in combining physiological and developmental theories of cell recognition and pattern formation.
Alipokuwa katika Chuo Kikuu cha Chicago, ambapo alitumia maisha yake ya kitaaluma (1895-1934), mtoto majaribio sana na invertebrates kama vile planarians flatworms na hydras maji safi, ambayo kuonyesha uwezo wa ajabu wa kuzalisha wenyewe kutoka vipande vidogo. Aligundua kwamba sehemu za kipekee, kama vile kichwa au mkia, kwa kawaida zilikua kutoka sehemu hiyo ya kipande ambapo sehemu hiyo hiyo ilikuwa imeunganishwa hapo awali, jambo linalojulikana kama polarity. Kulingana na majaribio yake, Child aliendeleza nadharia ya antero-posterior dominance, akisema kwamba shughuli za kisaikolojia katika viumbe vingi huongezeka kwenye mhimili wake kutoka chini hadi juu (au mkia hadi kichwa), na kwamba gradient hii ya shughuli katika kipande cha tishu huamua nafasi ya miundo inayokua kutoka kwake. Alihisi kwamba mwinuko huo ulisababishwa na utendaji wa kemikali kwenye utendaji wa chembe. Ingawa Child hakuweza kuonyesha jinsi gradients zilivyoundwa, nadharia yake iliwaongoza wachunguzi wengi kutafuta kuelewa michakato ya maendeleo katika maneno ya fizikia na kemikali. Mtoto alikuwa hasa ushawishi katika kuchanganya nadharia za kisaikolojia na maendeleo ya utambuzi wa seli na muundo wa muundo.