The automatic evaluation of children's reading performance by detecting and analyzing errors and disfluencies in speech is an important tool to build automatic reading tutors and to complement the current method of manual evaluations of overall reading ability in schools. A large amount of speech from children reading aloud plentiful in errors and disfluencies is needed to train acoustic, disfluency and pronunciation models for an automatic reading assessment system. This paper describes the acquisition and analysis of a read-aloud speech database of European Portuguese from children aged 6-10 from the first to fourth school grades. Towards the goal of detecting all reading errors and disfluencies, we apply a decoding process to the utterances using flexible word level lattices that allow syllable based false starts and repetitions of two or more word sequences. The proposed method proved promising in detecting corrections and repetitions in sentences, and provides an improved alignment of the data, helpful for future annotation tasks. The analysis of the database also shows agreement to government defined curricular goals for reading.