A number of studies done concerning the language of instruction and students‟ performance in secondary schools show the deterioration of education standards. Tanzanian children receive seven years of primary education in Kiswahili medium which is now becoming the first language of many children especially those who live in urban areas.
But in rural areas, Kiswahili is still a second language to many children after their vernacular languages. English is taught as a compulsory subject in primary schools from class one instead of class three which was the case some years ago. As the children complete their primary education and continue to secondary school the switch from Kiswahili to English is difficult for most of them. Criper & Dodd (1984) in Rubagumye (1990) after their research concluded that the level of English in secondary schools was completely inadequate for the teaching and learning of other subjects and immediate measures were to be taken.
Roy-Campbell and Qorro (1997) identify two problems that result from using English as a language of instruction in secondary schools; first, little knowledge is gained from the subject matter since learners do not understand English well, and second, even their Kiswahili language skills tend to be lagging behind because they are not using the language as a medium of instruction. Furthermore, learners are restricted from adequately acquiring the necessary knowledge, skills, and attitudes intended for their academic studies because of using a foreign language as a medium of instruction.
The language problem can be traced braced back to the time when Tanzania decided to adopt African socialism (Ujamaa) and as a result of this, there was a move of Africanization where everything that had to do with the colonial heritage was seen as a means to corrupt the socialist system. English language also was inherited from the British therefore was seen as a negative influence especially when Kiswahili officially became the medium of instruction in primary schools in 1967. English still remained the medium of instruction in secondary and tertiary education but was not given as high prominence as Kiswahili.
However, in 1969 the Ministry of National Education sent out a circular to all heads of secondary schools which explained the possibility of introducing Kiswahili as the language of instruction in some subjects starting with Political education in 1969/70, then Domestic 2 science in 1970, followed by History, Geography, Biology, Agriculture and Mathematics in 1971.
My interest in doing research on this issue has to do with my personal experience of teaching in both urban and rural secondary schools during fieldwork. In my experience, I saw that the ability of students in using the language of instruction in class was very minimal and so was their performance based on class tests.