At the 2009 RES conference I also discussed Chang-Tai Hsieh and Peter Klenow‘s “What have we learned about Growth?”. My comment focused on the contribution of schooling to development accounting. I argued that the development accounting framework is not well suited for the scenario where different schooling levels are imperfect substitutes (which seems the relevant case). But, maybe surprisingly, the answers of development accounting turn out to be quite accurate answers to a slightly different question: how much would productivity rise if poor countries were to close (only) the schooling gap with rich countries? (Unfortunately the answer is “not much.”) My slides are available in ppt and pdf.