The purpose of this study was to utilize an invented rule with English language learners (ELLs) in a clinical setting to determine differences based on language and age of the children. The performance was correlated with teacher reports of strong and weak language learning. Using a within-participants design, ELLs of age three to five were taught to apply a nonsense morpheme to signal a semantic difference. The invented rule was taught and responses were elicited in both English and English with Spanish interpretation. No significant difference for language was identified. Effect sizes for age were large (English, eta = 0.389, and English + Spanish, eta = 0.430) with five-year-old participants more likely to apply the rule to novel stimuli regardless of language. The performance of the majority of the participants correlated with teacher reports. The invented rule may provide a mechanism for assessing processing independent of prior language knowledge.