- 56 - States Parties shall use their best efforts to ensure recognition of the principle that both parents have common responsibilities for the upbringing and development of the child. Parents or, as the case may be, legal guardians, have the primary responsibility for the upbringing and development of the child. The best interests of the child will be their basic concern (bold added).348 347 Cf. Civil Code of Guatemala, October 9, 1963, art. 253 (evidence file, folio 3469). 348 Convention on the Rights of the Child, art. 18(1). 349 Convention on the Rights of the Child, art. 9(2). 350 Cf. Case of Fornerón and daughter v. Argentina, supra, para. 119.