14. A computer-implemented system for assessing spontaneous speech pronunciation, comprising: a processor; a non-transitory computer-readable memory comprising instructions for causing the processor to perform steps including: performing speech recognition on digitized speech using a non-native acoustic model trained with non-native speech to generate word hypotheses for the digitized speech; performing time alignment between the digitized speech and the word hypotheses utilizing a reference acoustic model trained with native-quality speech to associate the word hypotheses with corresponding sounds of the digitized speech; calculating statistics regarding individual words and phonemes of the word hypotheses based on said alignment; calculating a plurality of features for use in assessing pronunciation of the speech based on the statistics; calculating an assessment score based on one or more of the calculated features; and storing the assessment score in a computer-readable memory.
26. The system of claim 14 , wherein second statistics derived from native-quality speech are utilized in calculating the plurality of features.