The present study is designed to investigate whether children's difficulties with subject-to-subject raising (StSR) are due to intervention effects. We examine English-speaking children's comprehension of StSR with "seem" and Spanish-speaking children's comprehension of StSR with "parecer" 'seem,' a configuration never before tested in this language. Spanish "parecer" is ambiguous between a functional verb, which does not select an experiencer argument, and a lexical verb, which requires an overt experiencer (e.g.. In the first part of this study, we consider the hypothesis that the experiencer argument of "seem" may induce intervention effects even when it is not overtly produced and find support for this claim--English-speaking children perform poorly on StSR both when the intervening experiencer is overtly expressed and when it is implicit; Spanish-speaking children, on the other hand, only perform poorly on StSR with lexical "parecer" but do well on StSR with functional "parecer." These results are in line with intervention accounts. The second part of this study aims to investigate whether these intervention effects are rooted in children's grammatical or processing deficits. Results from a verbal processing task suggest that for a group of children--those who perform at chance or above on the StSR task--comprehension of sentences with an intervening experiencer is modulated by processing capacity. However, for those who consistently obtain a non-adult-like interpretation of StSR, processing capacity does not positively correlate with their performance. We hypothesize that, for this group, the difficulty is instead grammar-based.