Describes dual language instruction models, and presents a paradigm for examining congruence among theoretical models, teacher beliefs, and actual classroom practices to determine program effectiveness. Examples illustrate implementation pitfalls. Analysis of Proposition 227 finds it to be a decontextualized procedural model; it has an incoherent mandate without basis in sound pedagogical principles. Appendix compares enrichment and compensatory models. (Contains 57 references.) (TD)