Flowers will provide confirmation of the ID, one way or another. The Cotyledons here flower once a year (different times though for very similar looking plants) and do well in day-long sun. Their leaves tend to be longer and more paddle shaped than C. arborescens (which might explain the Kalanchoe suggestion). There can be quite a bit of variation in this aspect as a number of interesting cultivars have been selected. With time the differences become more apparent... the plant in the picture is still quite young. I would recommend providing much more light for a more compact form and better flowering down the road.
