Learning a foreign language in a natural immersion context with high exposure to the new language has been shown to change the way speech sounds of that language are processed at the neural level. It remains unclear, however, to what extent this is also the case for classroom-based foreign language learning, particularly in children. To this end, we presented a mismatch negativity (MMN) experiment during EEG recordings as part of a longitudinal developmental study: 38 monolingual (Swiss-) German speaking children (7.5 years) were tested shortly before they started to learn English at school and followed up one year later. Moreover, 22 (Swiss-) German adults were recorded. Instead of the originally found positive mismatch response in children, an MMN emerged when applying a high-pass filter of 3 Hz. The overlap of a slow-wave positivity with the MMN indicates that two concurrent mismatch processes were elicited in children. The children's MMN in response to the non-native speech contrast was smaller compared to the native speech contrast irrespective of foreign language learning, suggesting that no additional neural resources were committed to processing the foreign language speech sound after one year of classroom-based learning.