Economics

That’s kind of loaded question. There are many differences but for the exam I could boil it down to two words for you;  subsistence level. Classical theory contends that any growth in gdp per capita above that nations mean reverting level, or subsistence level, will cause a people to feel wealthier and hence be able to afford more babies. More babies, more people, bigger population which is a larger denominator in the gdp per capita ratio. Bringing us back to subsistence. This is not supported in empirical evidence though.  

Sticking with the high level concepts. Neoclassical in 4 words….steady state growth rate. They contend that all nations have a steady state growth rate where further capital deepening will not improve productivity. The way to increase productivity per unit of labor is via TFP (technology) aka total factor productivity. Know the formula TFP/labor share of gdp. This is the steady state growth rate.