A well educated teacher is a must !
Someone learning Spanish in the Dominican Republic just talking to people after some time will be able to understand and to talk the local language but to be well equipped to communicate in other Spanish speaking countries it is indispensable to learn basic grammatical rules. A high percentage of Dominicans because of the lack in education simply do not know good Spanish. For that reason even in practically all Dominican newspapers (most of the journalists are also uneducated in this sense) you will find a lot of grammar mistakes not to talk about orthography. Newspapers published in Argentina, Chile, Mexico, Cuba, Colombia and many more hispanic countries (also third world countries) do have a much higher standard. It makes no sense to learn the Dominican language if you have the chance to learn good Spanish.