Only underprivileged second language
instruction contexts experienced the problems of
inadequate mastering of the language that was the medium of
instruction, generating learning and understanding difficulties
and hampering the general acquisition of science literacy [17,
18]; the awareness of these consequences prompted the
recognition that the shift to mother tongue instruction would
be fundamental for development [19, 20] − an inference whose
validity is continuously confirmed by the analysis of the
difficulties encountered by science students [21−24].