This "Science Note" presents a study by Christopher Talbot and Lydia Yap, who teach IB Chemistry at Anglo-Chinese School (Independent), Republic of Singapore, to pre-university students. Pre-university students may postulate the correlation between the magnitude of the lattice enthalpy compound and its melting point, since both quantities are related to the strength of ionic bonding. This expected correlation appears to be falsified for magnesium oxide (melting point of 2800 degrees C) and aluminium oxide (melting point of 2000 degrees C). The melting point of aluminium oxide "appears" to be unexpectedly low and the lattice enthalpy of aluminium oxide "appears" to be unexpectedly high. Lattice enthalpy relates to the endothermic process for one mole of a solid ionic crystal breaking into gaseous ions (at infinite distance apart). (Contains 2 figures.)