Behavioural (or "behavioral") theory in psychology is a very substantial field: follow the links to the left or right for introductions to some of its more detailed contributions impinging on how people learn in the real world. How I have the effrontery to produce a single page on it amazes even me, whatever my reservations about it!

Behaviourism is primarily associated with Pavlov (classical conditioning) in Russia and with Thorndike, Watson and particularly Skinner in the United States (operant conditioning). 

• Behaviourism is dominated by the constraints of its (naïve) attempts to emulate the physical sciences, which entails a refusal to speculate about what happens inside the organism. Anything which relaxes this requirement slips into the cognitive realm. 

• Much behaviourist experimentation is undertaken with animals and generalised. 

• In educational settings, behaviourism implies the dominance of the teacher, as in behaviour modification programmes. It can, however, be applied to an understanding of unintended learning.

For our purposes, behaviourism is relevant mainly to: 

•  Skill development, and

• The "substrate" (or "conditions", as Gagné puts it) of learning

Classical conditioning:

is the process of reflex learning—investigated by Pavlov—through which an unconditioned stimulus (e.g. food) which produces an unconditioned response (salivation) is presented together with a conditioned stimulus (a bell), such that the salivation is eventually produced on the presentation of the conditioned stimulus alone, thus becoming a conditioned response. 

This is a disciplined account of our common-sense experience of learning by association (or "contiguity", in the jargon), although that is often much more complex than a reflex process, and is much exploited in advertising. Note that it does not depend on us doing anything.

Such associations can be chained and generalised (for better of for worse): thus "smell of baking" associates with "kitchen at home in childhood" associates with "love and care". (Smell creates potent conditioning because of the way it is perceived by the brain.) But "sitting at a desk" associates with "classroom at school" and hence perhaps with "humiliation and failure"... 

This site goes further into Watson's ideas, beyond Pavlov, and the "Little Albert" experiment.

Operant Conditioning

If, when an organism emits a behaviour (does something), the consequences of that behaviour are reinforcing, it is more likely to emit (do) it again. What counts as reinforcement, of course, is based on the evidence of the repeated behaviour, which makes the whole argument rather circular.

Learning is really about the increased probability of a behaviour based on reinforcement which has taken place in the past, so that the antecedents of the new behaviour include the consequences of previous behaviour.

Summary of Skinner's ideas On operant conditioning Skinner's own account Wikipedia on operant conditioning And here with diagrams of experimental set-ups and video

The schedule of reinforcement of behaviour is central to the management of effective learning on this basis, and working it out is a very skilled procedure: simply reinforcing every instance of desired behaviour is just bribery, not the promotion of learning. 

Withdrawal of reinforcement eventually leads to the extinction of the behaviour, except in some special cases such as anticipatory-avoidance learning.

Notes

Two points are often misunderstood in relation to behaviourism and human learning:

• The scale: Although later modifications of behaviourism are known as S-O-R theories (Stimulus-Organism-Response), recognising that the organism's (in this case, person's) abilities and motivations need to be taken into account, undiluted behaviourism is concerned with conditioning and mainly with reflex behaviour. This operates on a very short time-scale — from second to second, or at most minute to minute — on very specific micro-behaviour. To say that a course is behaviourally-based because there is the reward of a qualification at the end is stretching the idea too far.   
• Its descriptive intention: Perhaps because behaviourists describe experiments in which they structure learning for their subjects, attention tends to fall on ideas such as behaviour modification and the technology of behaviourism. However, behaviourism itself is more about a description of how [some forms of] learning  occur in the wild, as it were, than about how to make it happen, and it is when it is approached from this perspective that it gets most interesting. It accounts elegantly, for example, for ways in which attempts to discipline unruly students actually make the situation worse rather than better.

• (This point is heretical!) For human beings, reinforcement has two components, because the information may be cognitively processed: in many cases the "reward" element is less significant than the "feedback" information carried by the reinforcement.

Applied to the theory of teaching, behaviourism's main manifestation is "instructional technology" and its associated approaches: click below for useful guides