This article draws on an approach that conceptualizes L2 learning difficulty in terms of implicit and explicit knowledge. In a study with first language Mexican Spanish university-level learners (n = 30), their teachers (n = 11), and applied linguistics experts (n = 3), we investigated the relationship between (a) these groups' difficulty judgements of 13 selected L2 English structures and (b) perceived learning difficulty and learners' actual performance on measures of implicit and explicit knowledge. Our findings show that experts' learning difficulty judgements did not lead to significant predictions, whereas the learners' own difficulty rankings correlated significantly with their performance on the measure of explicit knowledge. Although correlations based on teachers' difficulty rankings did not reach statistical significance, the judgements of this group were the only ones that showed trends toward successful prediction of learners' performance on both the implicit and the explicit L2 measures. Thus the teachers exhibited a trend toward the best overall prediction ability.