The purpose of the work reported in this paper is to contribute to the knowledge about language acquisition. The paper itself informs about the running research as well as it summarises a part of the data received from the vocabulary sub-test repeatedly assigned to the sample of primary school children in the Czech Republic. It also touches the problem of subjective vocabulary arrangement in children, the individual differences in logic structures, associations and mechanisms of children searching for words as well as individual personality differences and family and social background influences on work with words. It also follows differences based on age.
  There are many studies dealing with the nature of mental growth and intelligence. However, mental processes are so complex that it has been difficult to determine their functional potentialities. In a broad sense, mental development includes the abilities in memory, imagination, language, percepts, concepts and problem-solving ability. Intelligence tests were developed in the early part of the 20th century in an effort to measure more accurately the mental abilities and potentialities of children as well as to follow the development and use of these devices. The complexity of mental development, however, makes the task of measuring in this area a very difficult one. In spite of that, information of the identifiable factors related to mental growth and development is necessary, it should be useful to teachers and others, to gain a better understanding of the mental development of children at different age levels.
  The present paper will concentrate on the area of language knowledge measuring, so, it is concerned especially with the following two of the above mentioned aspects:
  Language development
  The development of concepts
  Both above mentioned items are closely connected with the development and acquisition of communication skills, aspects of which can be registered also due to vocabulary tests and vocabulary sub-tests within intelligence tests.
  Language development of a pre-school child is an interpersonal and a highly spontaneous process based mainly on the interaction with adults. It is first of all the experience of language within the family and during pre-school years that elicits and modifies further language behaviour. Variations in environment, particularly variations in the interaction between the parents and the infant, influence idiolect of the child. As a listener and speaker interacting with mature language users, the child is able to learn very quickly an enormously complex set of rules of spoken language. Thus, when the child enters school, his comprehensible speech is well established. Many studies have shown that there is also the continuous increase in the size of children’s vocabulary during childhood. Studies of qualitative aspects of the vocabulary of children at different age levels reveal also a growth in the character of the word definition.
  An important aspect of the child’s mental development in connection with language skills is the acquisition of concepts. In the development of a concept, it is first necessary for the learner to recognise the essential features of an object as well as to vary the special features found. Through a wide range of experience a learner has to recognise the quality that characterises relevant objects in general. Children normally acquire a number of concepts before entering school. They are rather broad in nature, including first of all things of concrete realities of their environment. It is a growing range of experience that is essential for concept development. A child does not acquire concepts by merely meeting words in context. Rather it appears that at all age levels the building of concepts needs a certain amount of actual experience.
  The part of the research that forms the basis of the empirical work reported in this paper tries to contribute to an understanding of mental processes related to language acquisition. It is connected with the work of the Prague Group of School Ethnography, operating in several Czech primary schools, searching for what influences has had the changing Czech educational system on children during the last decade. One of the tools used by the researchers in these consequences is the Fourth Revision of the Binet Test.
  Thus, what I am predominately interested in here is the vocabulary growth and especially qualitative aspects of the vocabulary in the same children of a concrete school class at the different age level during their primary school attendance. The basis of this part of the research is the vocabulary sub-test of the above mentioned Fourth Revision of the Binet Test which has been administrated. The definitions given by the children were studied for this purpose, first of all for their completeness and qualitative nature. The group tested consisted of about 30 children (the number changes during years, due to fluctuation of the children within the monitored class). Till now the pupils have been tested for three years, from the third to the fifth class. Also they are monitored from the other points of view, case studies are created, social background is taken into account, etc. The majority are on or slightely below or above the average in intelligence. The comparable sample of other 90 parallelly tested school children is available.
  As far as the qualitative aspects of responses is concerned - the definitions given from year to year by the same children were studied for they completeness and qualitative nature - in agreement with literature we can describe a growth in the character of word definition as the growth from the descriptive type through the explanation one to the synonym type of response. It can be attributed to the enlarging of the vocabulary and the growing ability to symbolise things in terms of similarities and opposites as a reflection of continuous intellectual development, increasing language experience as well as school influence. A special kind of response was noticed in cases where the children do not know the word at all and they guess the meaning merely on the basis of the formal structure of the word (unknown word saze /soot/ - is defined as ”something like” sazenice /seedling/ for example). In evaluating the responses the part of speech characterisation as well as the concrete or abstract nature of words have been taken into account.
  The other interesting aspect of the present work is the sociological aspect. All children are from families of a lower socio-economic and educational status. In studies at the pre-school level, it has been noted that there is a relationship between children’s language and the socio-economic status of the family. They say that children of a higher socio-economic status tend toward language characterised by meaningful communication. They use longer units, with a greater variety of words. No difference was observed in the total number of words used. The differences can be found mainly in the level of care and attention the parents pay to their children.
  In these consequences we can thus understand that one of the highest vocabulary sub-test results has a dressmaker’s and driver’s daughter who is always given a great amount of time and guidance from her mother. But… Why the best (and really good) results has always had the boy who ”hates” mother language lessons and whose school results are not very good, the neglected but gifted mathematician whose childhood is full of problems? We would like to find an answer.
  Language development of young school children is still one of the important as well as interesting indices to their intellectual development. The development of language follows the principles characteristic of other aspects of development. It emerges as a result of both maturation and learning and involves the acquisition of new language devices as well as the refinement of language devices already acquired.