General difference
L1 – natural learning
L2 – learning in the classroom
The setting
the number of people the learner meets; while the native child is limited to parents, family, and friends
the L2 learner may encounter one native speaker or teacher at a time or several
Consequently the kinds of relationship the L2 learner has with the people he meets may be wider than those of the L1 learner
the exposure
in L2 learning it may range from accidental or even random to highly structured
in L1 learning it is limited by the ways in which children are brought up in a particular culture and by the adult's beliefs about how they should talk to children
in the first language exposure is fairly constant
in the second language it can vary from occasional to regular (but widely spaced) to 'immersion'.
the learner
second languages are learnt later than first languages
so L2 learners are usually older than L1 learners and hence exhibit more mature cognitive and emotional development
for instance teenagers and adults can use more conscious mental processing than the intuitive processing of the child
motivations and attitudes
it is hard to say exactly what motivates a child to learn his first language
L2 is usually learnt for a purpose
Literacy
L2 learners have often learnt to read and write in their first language and this causes them to approach language learning in a different way
L1/L2 differences
The child's language system is a system in its own right rather than an incomplete version of the adult system.
The learner speaks an 'interlanguage' which has a system of its own; unlike the child, a second language learner more often than not fails to develop his system completely into the target and it becomes 'fossilised'.
A child’s language is involved in his developing cognitive structure, emotional states, relationships, and play.
It is not true for SLA unless engineered (e.g. pen-friends and foreign visits).
The learner will be acquiring a set of skills to do a job with, and/or a new way of looking at the world derived from the new culture.
How much of either he gains will depend on his needs and interests.
The use of the first language goes hand in hand with the child's needs and interests.
This will also be true of classroom L2 learning when it occurs in a situation where the learners have to make immediate use of the language outside the classroom
it has much less application to teaching situations where the language does not have an immediate practical value - the typical situation of a foreign language classroom in England.
The child's use and learning of language is partly determined by mental capacity
the differences from the child relate to the greater cognitive and emotional maturity of the L2 learner.
Teaching
Teaching: language is usually taught ‘bit by bit.’
Teaching materials and techniques have to take into account the various forms of mental limitation.
There are particular stages in language development through which all children progress, even if the rate of progression varies.
Specific stages of development have been acknowledged in also SLA, although they differ from acquisitional sequences exhibited in FLA.
Learners from the same L1 background will develop the L2 in a similar way.
teaching sequences that go counter to the order of acquisition that has been discovered should be avoided.
The child learns to adapt its language use to particular social situations.
Since the audience in the classroom is largely restricted to the teacher and fellow learners, it is reasonable to assume that initially there is less encouragement for the L2 learner to acquire flexible language.
Even advanced learners tend to import informal expressions into tasks in which they are not appropriate.
the use of role-playing may enhance the learner’s flexibility with respect to register.
Teaching: the classroom needs to present a greater variety of language and to use techniques in which pupils and teachers adopt a variety of roles.
if the pupils are never allowed to initiate questions or give orders in the second language, they cannot be expected to learn to do so.
if it is true that L2 learners profit from conversational interaction as L1 learners do, then a way needs to be found of bringing opportunities for such interactions into the classroom.