Child Development

spite arbitrary transformations. In the classic
Piagetian conservation of liquid task, children are
presented with two identical containers holding equal
amounts of liquid. Liquid from one of the containers
changes in appearance by being poured into a taller,
narrower container. The children are asked to judge
the equivalence of the transformed liquid and the liq-
uid that remained in its original container, and to jus-
tify their answer. A child who grasps conservation is
able to take two dimensions into account simulta-
neously and therefore understands that the change in
the height of the transformed liquid is compensated
for by the narrower width. That is, despite changes in
appearance, the quantity of liquid remains the same.
An understanding of conservation marks the pres-
ence of Piaget’s concrete operational stage of cogni-
tive development, usually reached between five and
seven years of age.

See also: PIAGET, JEAN

Bibliography
Diamond, Nina. ‘‘Cognitive Theory.’’ In Benjamin Wolman ed.,
Handbook of Developmental Psychology. Englewood Cliffs, NJ:
Prentice-Hall, 1982.
Donaldson, Margaret. ‘‘Conservation: What Is the Question?’’ Brit-
ish Journal of Psychology 73 (1982):199–207.
Rebecca M. Starr

CONTRACEPTION

Contraception refers to the use of hormones, surgery,
physical devices, chemicals, fertility awareness, or
breast-feeding to prevent pregnancy. Contraceptive
methods and the prevalence of use vary substantially
around the world. Modern methods predominate in
North America, led by female sterilization (34% of all
use), oral contraceptive pills (21%), male sterilization
(20%), and condoms (14%). Female sterilization in-
volves surgically removing part of the fallopian tubes
or blocking them with clips, rings, or heat destruc-
tion. Similar techniques on the vas deferentia (sper-
matic ducts) sterilize men. Oral methods combine
estrogen with progestogen, normal female hormones,
to prevent ovulation, or use progestogen alone to
make cervical mucus hostile to sperm penetration.
Barrier methods create a barrier between ovum and
sperm and are often combined with chemicals that
kill sperm (spermicides) to increase effectiveness.
Male condoms cover the penis, female condoms line
the vagina, and diaphragms or caps cover the cervix.
Other methods include hormonal injections or im-
plants; intrauterine devices that block implantation of
a fertilized egg; periodic abstinence during the time
of the menstrual cycle when a woman is most likely to
be fertile; and withdrawal of the penis, prior to the re-
lease of sperm.

See also: ARTIFICIAL INSEMINATION; BIRTH;

PREGNANCY

Bibliography

United Nations, Department of Economic and Social Affairs, Popu-

lation Division. ‘‘World Contraceptive Use in 1998.’’ In the

United Nations [web site]. Available from http://www.

undp.org/popin/wdtrends/wcu/fwcu.htm; INTERNET.

Philip Hannaford

COOPERATIVE LEARNING

Cooperative learning refers to a variety of instruction-

al strategies in which students work in small, usually

mixed-ability, groups and are expected to help one

another learn academic material or complete projects

together. There are many forms of cooperative learn-

ing that are often used in elementary schools. Stu-

dents may simply be asked to work together, without

any particular structure or goal. But cooperative

learning research finds greater success when groups

have reward interdependence, task interdependence,

or both. Reward interdependence means that group

members can achieve success only if the whole group

accomplishes some objective. For example, groups

may be evaluated based on the sum or average of indi-

vidual quiz scores or average ratings of individual

products, or based on an evaluation of a common

product, such as a report, a mural, or a project to

which all group members contributed. The group’s

success may be recognized by the teacher using

praise, certificates, or other symbolic rewards, or it

may count toward a portion of children’s grades. Task

interdependence exists when each group member is

responsible for a unique portion of a group task, and

the group cannot meet its goal unless all students do

their parts.

Cooperative learning can be used in every subject

and at every age level. Research has found that coop-

erative learning can increase academic achievement,

especially if there are group goals or rewards and if

the only way groups can achieve their goals is if all

group members have learned the material being stud-

ied (as demonstrated on individual quizzes, composi-

tions, or other products). This structure causes

students to teach each other, to assess each other’s un-

derstanding, and to encourage each other to excel.

Peer teaching, which is beneficial both to the child

who teaches and to the child being taught, and peer

encouragement are the main explanations research

has identified for the achievement effects of coopera-

tive learning. Research has also identified positive

effects on outcomes such as intergroup relations, atti-

tudes toward mainstreamed classmates, self-esteem,

and general attitudes toward school.

See also: LEARNING

COOPERATIVE LEARNING 99