The main purpose of this paper is to construct a model of economic growth that is consistent with the growing body of evidence on convergence. We want in particular to explain gradual convergence in output and income per person while allowing for an international credit market that equates the real interest rates across economies. The key to our model is that capital is only partially mobile: borrowing is possible to finance accumulation of physical capital but not accumulation of human capital. We show that the assumption of partial capital mobility imbedded in an open-economy version of the neoclassical growth model can explain the evidence on convergence. Perhaps the model in this paper is best applied not to countries or even states but to families. The model may in this context be useful for explaining the dynamics and distribution of wealth. It would predict that the most patient families would tend to be the most highly educated and they would own most of the economys physical capital. Physical non-human wealth would be more highly concentrated than human wealth. (authors)