Sentence:  But to myself I thought: ‘Considering that for eight whole years I sat on the front bench as top of the class while he drifted about somewhere in the middle, he can hardly fail to nourish a wish, left over from his schooldays, that some day or other I may come a complete <WSD>cropper</WSD>.' 
Meaning of the word marked with <WSD> tags:  A fall, a tumble.